EFFECTS OF POISSON'S RATIO ON FAILURE MODE AND OVERALL DEFORMATIONAL CHARACTERISTICS OF A ROCK SPECIMEN

Using FISH functions written in FLAC to calculate the overall deformational characteristics, the effects of Poisson's ratio in the elastic stage on the failure mode and overall deformational characteristics were modeled for a rock specimen with a material imperfection in plane strain compression. In the elastic stage, the adopted constitutive relation of rock was linear elastic; and in the strainsoftening stage, a composite Mohr-Coulomb criterion with tension cut-off was used and the post-peak constitutive relation was also linear.The increased Poisson's ratio in the elastic stage leads to a transition of failure mode from single to complex shear fractures and a larger failed area is expected.The predicted shear band inclination is lower at a higher Poisson's ratio in the elastic stage, which cannot be explained by Coulomb, Roscoe and Arthur theories.Prior to the peak stress, the calculated slopes of the linear stress-axial strain curves, stress-lateral strain curves, lateral strain-axial strain curves and volumetric strain-axial strain curves at different Poisson's ratios in the elastic stage are consistent with the linear elastic solutions in plane strain compression.The calculated Poisson's ratio in plane strain compression is higher than 0.5 if the adopted Poisson's ratio in the elastic stage exceeds 1/3, as is confirmed by the present numerical simulation.At a higher Poisson's ratio in the elastic stage, the post-peak lateral strain-axial strain curve, volumetric strain-axial strain curve and calculated Poisson's ratio-axial strain curve become less steep; whereas the post-peak stress-lateral strain curve becomes steep and the precursor to failure is less apparent.